1. Technical Field
The present invention relates to a steering lock unit for locking a steering wheel of vehicle and so on.
2. Description of the Related Art
Conventionally, a steering lock unit for locking a steering wheel is employed to prevent the theft of a vehicle and so on. Typically, in the steering lock unit, when a lock shaft enters a recess formed on the outer surface of a steering shaft coupled to the steering wheel, the steering wheel becomes locked. When the shaft escapes the recess, the steering wheel becomes unlocked.
The conventional power steering lock unit has only one drive system of the lock shaft, and thus it is difficult to achieve a balance between an operating speed and an extracting force of the lock shaft. For example, a steering lock unit disclosed in patent document JP2006-15984A adopts a system in which movement of a cam follower along a cam groove allows the lock shaft to move back-and-forth relative to the steering shaft. The inclination angle of the cam groove is made gentle and steep to provide an operation range that places priority on the operation speed of the lock shaft and an operation range that places priority on the extracting force of the lock shaft.
In patent document JP2004-106750A, there is disclosed a steering lock unit in which a lock position and an unlock position of the lock shaft are detected using two detecting switches and also a correct position of the lock shaft on an intermediate area between the lock position and the unlock position can be accurately detected using a resistance change measuring device.
However, in the steering lock unit of JP2006-15984A, in spite of an engagement state of the lock shaft and the steering shaft, the lock shaft normally performs a constant operation at a predetermined position. However, it is not possible to perform an operation by placing priority on any one of the operating speed and the extracting force of the lock shaft according to the engagement state.
In the steering lock unit of JP2004-106750A, although the correct position of the lock shaft on the intermediate area can be detected using the resistance change measuring device, it is necessary to provide the resistance change measuring device and accordingly provide on the outer surface of the lock shaft a special coating of which resistance varies in a continuous or stepwise manner. However, this arrangement is disadvantageous because the construction becomes complicated and the cost becomes higher.
Further, in the steering lock unit of JP2004-106750A, a projection provided in a lateral direction on the side surface of the front end of the lock shaft operates a lock state detecting switch while a projection provided rearward in a longitudinal direction (i.e. in a moving direction of the lock shaft) operates an unlock state detecting switch. Therefore, it is necessary to dispose the two detection switches separately more than at least a distance obtained by adding a stroke of the lock shaft to a length between the position of the lock state detecting switch and the tip end of the projection on the rear end of the lock shaft. This constitutes an obstacle regarding the design for downsizing the steering lock unit.